Research On Surface Damage Of GaAs Induced By Continuous And Nanosecond Pulse Laser

Since the invention of laser in 1960s, the interaction of laser with materials has been being an interesting and important research field. It is useful in many scopes, such as laser processing, laser weapons, laser asistted nuclear fusion, laser annealing, laser deposition, laser ablation, breakdown of optical units, detectors damage, et al. The semiconductor devices and materials generally work under intense laser and irradiation and there is much danger of being damaged and out of function. For example, radars and optoelectronic detectors are the main object of laser weapons in the war, solar cells are widely used in outer space and facing various cosmic radiations, the damage usually is generated when annealing in ion-implanting of semiconductor. Cosequently, the study on laser damage and interaction of intense laser with semiconductor materials is greatly practical and significant.GaAs is the second important semiconductor after Si and the widely used in microelectronic, luminescent and optoelectronic devices. It is the most important materials for fabrication of light-emitting diode (LED), laser diode (LD), solar cell (SC), high speed integrated circuit (IC), and high frequencied microwave divices under high temperature. Furthermore, GaAs is also used in optical field as infrared laser output coupler, saturable absorber for passive Q-switch, and frequency converting unit. The study of laser induced damage on GaAs is very necessary and much valuable. This research topic has been being active and attractive since 1970s. Much work on it has been carried out and many achievements were gained. The work includes the studies of laser with various wavelengths and frequencies with GaAs material and devices. However, there are lots of work needs to be done or to be carried out comprehensivly, such as the interaction of GaAs with continuous laser at short wavelength, the elemental compont change induced by laser irradiation, et al.In this dissertation, we mainly studied the interaction of intense cw and nanosecond pulse laser with GaAs materials around the damage threshold. The surface damages of GaAs single crystals induced by cw and nanosecond pulse irradiation with 0.53 and 1.06μm wavelength were studied experimentally and theoretically. The corresponding damage thresholds were determined. The damage morphologies and elemental components were detected by electronic probe microanalyzer (EPM). The damage mechanism was analysized comprehensively. The primary research work is listed as follows:Ⅰ. The experimental study on laser induced damage of GaAs by 0.53μm continuous laser was carried out for the first time. In the experiment the irradiation beam served as a probe beam simultaneously. The damage process was probed in real time. The damaged morphologies and elemental components were detected by EPM, as well, finding that the foremost detectable damage was thermal decomposition and As content decreased simultaneously. The following severe surface damage occurred in the form of surface melting and evaporation with intense oxidation. The damage threshold curve was plotted. The theoretically calculation was performed by using finite difference method and good results were obtained which indicated the exact thermal damage mechanism.ⅡThe laser induced damage on GaAs by 1.06μm continuous irradiation was investigated. A separate probe beam by He-Ne cw laser was utilized to monitor the damage process in real time. The damage morphologies and elemental components were detected as well. Only a very faint decrease of As component was detected during the whole damage process and no oxidation was found. Note that the damage threshold was greatly dependent on the boundary condition. The theoretical explanation was presented and analyzed based on the thermal damage mechanism.Ⅲ. The surface damage of GaAs induced by 0.53μm nanosecond pulsed laser was investigated experimentally and theoretically. The single shot and multishot damage experiments were carried out and corresponding damage thresholds were determined. The damage morphologies and elemental contents were detected as well. The damage morphology was different from that by 1.06μm nanosecond pulses in the absence of small localized pits before uniform melted crater. The melted depth was very faint. The elemental contents showed no evident change for laser irradiation around the damage threshold. According to the thermal heating mechanism we made the theoretical analysis and calculated the temperature profile of the irradiated GaAs surface by using finite difference method. The results showed good agreement with experiment.Ⅳ. The laser induced damage of GaAs by 1.06μm nanosecond pulsed laser were studied. The singe shot (1-on-1) and multishot (s-on-1) damage experiments were carried out and the corresponding damage threshold were measured. The damage morphological observation showed that some localized small pits emerged before the uniform melted crater. The elemental analysis showed no evident Ga-riched phase at the damaged region under the medium irradiated fluence just above the damage threshold. The temperature estimation using finite difference method based on thermal heating model only reached several decades degrees rise of material surface which is much smaller than the melting point of GaAs. Therefore, the uniform heating damage mechanism is not the primary damage mechanism for laser irradiation with photo energy less than the band gap. Combining with the multishot damage we proposed a microdefect accumulation enhanced absorption mechanism to explain the instance.In brief, we completed four experiments on laser induced damage of GaAs single semiconductor materials. The 0.53μm cw laser irradiation damage process of GaAs is investigated for the first time. The damage process was monitored in real time by probed with the same irradiation beam. The foremost detectable damage is decoposition of GaAs surface layer with a Ga-riched phase left. Evident melting process and oxidation phenomenon were found. While the damage by 1.06μm cw laser whose photon energy is just less than the band gap of GaAs at room temperature show much difference from that by 0.53μm cw laser. During the whole damage process no evident change of elemen contents was found where only very faint decrease about less than 1% in proportion of As content can be detected. The thermal decomposition of GaAs surface could be detected by monitoring the reflectivity and optical distribution of the reflected probe beam in real time. Evident melting and oxidation were not discovered. The damage threshold was greatly dependent on the boundary condition. The above differences for two cases are attributed to the distinct photon energy of two laser wavelengths so as to the distinct aborption process. The nanosecond laser damages on GaAs by 0.53 and 1.06μm irradiation were also conducted. The induced difference was the absence of previously emerged small localized pits before the uniform melted crater for laser with shorter wavelength. The appearance of the pits was obviously relevant with the surface defects. The theoretical calculation of surface temperature profile showed the thermal heating mechanism was dominating for laser induced damage by laser with photon energy above the band gap. In the contrary, the thermal heating model was not fit to explain the damage induced by laser with photon energy below the band gap. The other damage mechanism must play important role in the damage process. Combining with the multishot damage the microdefect accumulation enhanced heating mechanism was proposed.